Behaviour-dependent changes of the acoustically evoked potential in the frontal cortex of the freely moving rat and modulation by electrical basal forebrain stimulation.

The behaviour-dependent and nucleus basalis magnocellularis (basal forebrain; bf) stimulation-induced modulatory influences on acoustically evoked potentials (AEP) in the medial frontal cortex (FC) of freely moving rats are described and compared. Bipolar stimulating electrodes were implanted within the bf and recording electrodes on the frontal cortex, area 10, the somatosensory cortex, area 3, the olfactory bulb, and in the nasal bone. Electrical single impulses with increasing intensities were applied within the bf 100 ms before or simultaneously with the click. The configuration of the FC-AEP and amplitudes of its components depending on spontaneous changes of the behavioural state. During grooming and exploration the prominent alterations in comparison to relaxed wakefulness are reductions of the amplitudes and shortening of the peak times of the AEP components. The bf stimulation simultaneously with the click caused amplitude reductions of all FC-AEP components. When the electrical stimuli were applied 100 ms before click, an amplitude reduction of the N21 component correlated with a shorter peak time of the N60 component was observed. These modulations are similar to AEP configuration during a certain type of spontaneous exploration. The bf-induced modulatory influences on the acoustic information processing within the FC are different immediately after bf stimulation and 100 ms later.